We begin here with that major revelation today from the wife of robin Williams. We've now learned that in his final days, Williams was dealing not only with depression and the battle to stay sober, but also something else. Something he wasn't ready to tell the world about. Tonight, nick watt bring the comedian's secret struggle. And nick sits down with the men telling the real story behind one of robin Williams' signature roles. Reporter: In his standup, robin Williams didn't shy away from his demons. You see, as an alcoholic, you will violate your standards quicker than you can lower them. You will do That even the devil would go, dude. Reporter: Today, his wife, telling the world of a battle Williams hadn't been ready to talk about. Robin's sobriety was intact, Susan Schneider said in a written statement. He was brave as he struggled with depression, anxiety and early stages of Parkinson's disease, which he was not yet ready to share publicly. Early Parkinson's consists of tremor and a little bit of slowness and perhaps postural changes. Reporter: It's often an integral part of the disease. 20% to 40% suffer severe depression. I wouldn't want to leave people that there's a relationship between Parkinson's and depression. People can be discouraged when they hear about the diagnosis. That's different than being depressed. Reporter: Michael J. Fox who was diagnosed with Parkinson's, tweeted, stunned to learn robin had P.D. Pretty sure his support for our foundation predated his diagnosis. A true friend. I wish him peace. Susan, Williams' widow, hopes might live in how he died. It's our hope in the wake of robin's tragic passing, that others will get the care and support they need to treat the battles they are facing, so they may feel less afraid. We want to give the thoughts and prayers to his family. Reporter: On Broadway, the cast of "Aladdin" and the man filling Williams' genie shoes, paid an appropriate tribute. You little genius, you. Reporter: Since robin Williams' death, it is this role, the genie in aladdin, that many are choosing to remember him by. Al, all joking aside, just be yourself. Reporter: The genie is a cartoon manifestation, voiced by Williams. I wanted to be him. Reporter: Drawn by animator Eric Goldberg, a movie made by our parent company, Disney. He just speaks to robin's immense abilities and warmth. 10,000 years will give you such a crick in the neck. Reporter: This was a role created for Williams, in a time before big movie stars voice animated movies and a time before real belly-laugh humor was a cornerstone of big-screen cartoons. But never duplicated. Duplica duplicated. Reporter: Robin Williams' genie changed all that. We were animators. Reporter: The directors took a risk and wrote the role for Williams. And to convince him to take it, Goldberg animated lines from an old Williams comedy album. Before we do the play, I want to talk about the serious subject of schizophrenia. I had the genie grow another head to argue with him in the animation. That clicked with him. There was a script. We started with a script. Aladdin. Nice to have you on the show. Can we call you Al? Maybe just din. When we got robin in the booth, if that's a road map, then robin took lots of detours. There's a popsicle stand. His energy would grow and grow and grow. Not bad. Good night, Alice. We were at a point, we have so much stuff. This is incredible. He would do, let me do it again. L Let's make some magic. Reporter: The world of aladdin, captured some of that magic. We didn't expect him to come back with all of the celebrity impressions the first time we recorded him. I never did it. I am not at fault. You need more power, Jim. Don't be afraid. You had it all along. So, we readapted. We incorporated robin's riffs into the fabric of the film. The ever-impressive -- all right, sparky, here's the deal. Not many people will recognize the impression of William F. Buckley. There's a few -- We work with some of them. That doesn't matter. And sometimes he would just say a hysterically funny line only once. And we would have to pluck it out. For example, when he was the bee. Stop it. Buzz off. You know, it was once. He only did it once. Okay. Fine. But remember, bee yourself. Yeah, right. He can do so much with his voice to make it expressive, to make it change, to make it be different characters. Reporter: And to have that voice attached to that brain. Yeah. Exactly. It's kind of a one-two punch there, really. Come on, kid, see? Got to get the snake, see? No substitutions, exchanges or refunds. A mind that was special and unique and went to places most of us have never been. The spirit and his passion and his connection to both the characters in the movie and the audience, I don't think that's going to dim over the years. Genie, I'm going to miss you. Reporter: Eric Goldberg drew this tribute to robin Williams. He was a real-life genie. And, boy, did he grant our wishes. No matter what anybody says, you will always be a prince to me. Reporter: I'm nick watt, for "Nightline," in Los Angeles.

This transcript has been automatically generated and may not be 100% accurate.

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